[SOLVED] How to route a pacemaker lead?

Hi all,
I need to route the leads of an artificial pacemaker along the subclavian vein, through the superior vena cava and eventually to the right ventricle. I have the human phantom ready (morphed Ella v3) and already placed the pacemaker housing above the left clavicle, and only toggle on the visibility of relevant organs (bones, veins & heart).
I am trying to route the leads with the spline tool; the points are always placed somewhere behind the vein, instead of snapping on it.
I appreciate any help, thanks!

Hi everyone, so I got an ad-hoc solution to this:
I created several solid objects (small spheres with radius 1mm) along the intended path and snapped the spline to those spheres. I don't know of any better way but it worked for me!

At IT'IS we typically use the planar cut tool and slice the model (e.g. vein) at multiple locations along some direction (e.g. z-axis). Then you can snap to the center of the vein. Here is a script to slice the selected entities:

import XCoreModeling
Vec3 = XCoreModeling.Vec3

make_manifold = False
normal = Vec3(0,0,1)
distance_between_slices = 10

selection = XCoreModeling.GetActiveModel().SelectedEntities
selection = [e for e in selection if XCoreModeling.IsTriangleMesh(e) or XCoreModeling.IsBody(e)]

p0, p1 = XCoreModeling.GetBoundingBox(selection)

def slice_entity(e, p0, p1, normal, distance):
    if XCoreModeling.IsTriangleMesh(e) and make_manifold:
    projected_len = (p1-p0).Dot(normal)
    len = 0.5 * distance
    while len < projected_len:
        p = p0 + len*normal
        slice = XCoreModeling.CreatePlanarSlice(e, p, normal, True)
        slice.Name = e.Name + "_%g" % len
        len += distance

for e in selection:
    slice_entity(e, p0, p1, normal, distance_between_slices)

Note: make_manifold may be useful if you slicing is not robust enough.

Thank you @bryn! I will adapt this to my needs.